Method for defining at least one characteristic curve of a pressure-medium-actuated brake system of a vehicle

ABSTRACT

A method for defining at least one characteristic curve of a pressure-medium-actuated brake system of a vehicle, the curve representing a relationship between a brake pressure and a brake demand, and for operating a pressure-actuated brake system of a vehicle, in which at least one brake cylinder can be supplied with a pressurized medium under a braking pressure, and in which the braking pressure is formed based on at least one such characteristic curve, and to a pressure-actuated brake system of a vehicle in which at least one brake cylinder can be supplied with a pressurized medium under a braking pressure.

RELATED APPLICATION INFORMATION

The present application claims priority to and the benefit of European patent application no. 21161401.1, which was filed in Europe on Mar. 9, 2021, the disclosure which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a method for defining at least one characteristic curve which, in a pressure-medium-actuated brake system of a vehicle, represents a relationship between a brake pressure and a brake demand, according to the description herein, a characteristic curve which has been defined according to such a method, according to the description herein, a method for operating a pressure-medium-actuated brake system of a vehicle, in which at least one brake cylinder can be supplied with a pressurized medium under a braking pressure, and in which the braking pressure is formed on the basis of at least one such characteristic curve, and a pressure-medium-actuated brake system of a vehicle in which at least one brake cylinder can be supplied with a pressurized medium under a braking pressure, according to the description herein.

BACKGROUND INFORMATION

Driver assistance systems can communicate a braking demand to such braking systems. This is usually done with the aid of an electrical brake demand signal, which specifies a target deceleration of the vehicle. The braking system can set this target deceleration using a closed control loop. For this purpose, the actual deceleration of the vehicle is determined via the measured wheel speeds, for example, and compared with the target deceleration. If the actual deceleration deviates from the target deceleration, brake pressure is increased or reduced accordingly. In this case, the brake demand signal usually covers a fixed range of values and, apart from special coding for error indication, has no deviating meaning. The value range is processed and interpreted by the braking system in the same way over the entire value range.

For autonomous driving of the vehicle, the demand on the control quality of the brake system increases. The control loop is often closed in a complex longitudinal deceleration controller, which can be located outside the brake system. Even though the direct controlled variable in the longitudinal deceleration controller does not have to correspond exactly to the physical variable (deceleration of the vehicle in m/s²) used by the brake system to close the loop, this is a known problem. In particular, due to the inertia of electro-pneumatic braking systems, requirements on the controller speed for a stable controller cascade cannot be met or can only be met to a limited extent.

For these reasons, in autonomous driving mode the braking of the vehicle requested by the longitudinal deceleration controller is often implemented by the electro-pneumatic braking system without a closed control loop, which leads to a largely linear relationship between the brake demand and the output brake pressure, at least at one operating point. However, disturbances such as road inclination, wind, etc. and assumptions that deviate from reality, such as the estimated vehicle mass, braking coefficient, etc., are still compensated for by the longitudinal deceleration controller, for example. For autonomous driving of the vehicle, it must be possible for the brake system to perform a requested braking with a high degree of safety and reliability.

SUMMARY OF THE INVENTION

An object of the invention is to enable a brake demand or request to be performed by the brake system with a high degree of safety and reliability.

This object may be solved by the features of the main embodiments, as described herein.

It may be assumed that a high level of safety and reliability of the overall system is ensured via a single variable which is transmitted, for example, as a brake demand or request from a longitudinal deceleration controller to the brake system (e.g. via CAN or other transmission systems).

In this case, a brake demand or request, which in particular originates from an autonomous driving system or from a driver assistance system, is interpreted and executed in a brake system, in particular an electro-pneumatic braking system, taking into account control and safety challenges. Here, on the one hand, the behavior of a closed control loop with a tendency to increase the brake demand in the case of an under-braked vehicle, the above-mentioned requirements on an electro-pneumatic braking system when executing autonomously generated braking demands, and the presence of redundant components in an electro-pneumatic braking system may be taken into account.

According to the invention, the value range of the brake demand signal is divided into several brake demand ranges, which may be into at least two brake demand ranges and further which may be into three brake demand ranges. However, more than three brake demand ranges may also be provided.

A first aspect of the invention presents a method for defining at least one characteristic curve representing a relationship between a brake pressure and a brake demand in a fluid-pressure-actuated brake system of a vehicle, comprising at least the following steps:

-   -   a) specifying a brake demand value range for the brake demand,         which includes a minimum brake demand, a maximum brake demand,         and intermediate values between the minimum brake demand and the         maximum brake demand,     -   b) defining a brake pressure value range for the brake pressure,         which includes a minimum brake pressure, a maximum brake         pressure and intermediate values between the minimum brake         pressure and the maximum (applicable) brake pressure,     -   c) defining at least two characteristic curve sections of the         characteristic curve, by:         -   c1) defining a first support point of the characteristic             curve at which a first brake demand limit value and a first             brake pressure are assigned to one another, the first brake             demand limit value lying within the brake demand value range             and the first brake pressure lying within the brake pressure             value range, and the first brake demand limit value             representing a minimum brake demand and the first brake             pressure representing a minimum brake pressure,         -   c2) defining a second support point of the characteristic             curve at which a second brake demand limit value and a             second brake pressure are associated with each other,             wherein the second brake demand limit value lies within the             brake demand value range and is greater in magnitude than             the magnitude of the minimum brake demand but less than the             magnitude of the maximum brake demand, and wherein the             second brake pressure lies within the brake pressure value             range and is greater than the minimum brake pressure but             less than the maximum (applicable) brake pressure,         -   c2) defining a first characteristic curve section of the             characteristic curve which extends between the first support             point and the second support point and which, in a first             brake demand range or area (I), represents the relationship             between the brake pressure and the brake demand,         -   c3) defining a third support point of the characteristic             curve at which a third brake demand limit value and a third             brake pressure are associated with each other, wherein the             third brake demand limit value lies within the brake demand             value range and is greater in amount or magnitude than the             amount of the second brake demand limit value but less than             or equal to the amount of the maximum brake demand, and             wherein the third brake pressure lies within the brake             pressure value range and is equal to the maximum             (applicable) brake pressure,         -   c4) defining a second characteristic curve section of the             characteristic curve which extends between the second             support point and the third support point and which, in a             second brake demand range or area (II), represents the             relationship between the brake pressure and a brake demand.

The brake demand value range and the brake pressure value range represent concluding ranges in this respect, because values outside these ranges are not possible or not provided for. In electro-pneumatic brake systems, for example, the reservoir pressure within a pressure reservoir always represents the maximum (applicable) brake pressure because no greater brake pressure can be generated compared to this reservoir pressure.

The invention therefore defines at least two characteristic curve sections of the characteristic curve or at least two brake demand ranges, which can be configured differently with regard to the respective assignment between the brake demand and the brake pressure resulting from the relevant brake demand. In particular, the at least two characteristic curve sections of the characteristic curve may have different gradients.

The characteristic curve or at least two characteristic curve sections of the characteristic curve or the at least two brake demand ranges are defined in particular independently of a vehicle deceleration-dependent brake pressure distribution between a front axle and a rear axle or between a right wheel and a left wheel. In such a known vehicle deceleration-dependent brake pressure distribution, it is taken into account, for example, that the rear axle deflects during braking and then the normal forces at the rear axle decrease, so that the rear axle would tend to brake lock if the brake pressure at the rear axle is not lowered relative to the brake pressure at the front axle, for example, once a certain limit deceleration is reached.

The advantages of the invention become apparent from the following description of practical examples.

In the case of partial braking, which is controlled here by the first characteristic curve section, for example, the longitudinal deceleration controller usually requests a relatively moderate deceleration of the vehicle, so that the brake request or demand then lies within the first brake demand range, for example. Depending on the estimated total vehicle mass, different first characteristic curve sections with, for example, different gradients are present or specified. Based on the first characteristic curve section of the characteristic curve assigned to the relevant vehicle mass, a specific brake pressure is then assigned to the moderate brake demand here. The longitudinal deceleration controller also measures the vehicle reaction in the form of the actual vehicle longitudinal deceleration and can adjust the brake demand and thus the brake pressure even in the event of relatively small changes in the actual longitudinal deceleration. This is done with little time delay, since the brake system itself need not have a longitudinal deceleration controller or a closed control loop.

In another example, it is assumed that the vehicle is under-braked because, for example, the total vehicle mass has been estimated too low, or because other assumptions, such as the braking effect of the trailer brake (characteristic pressure to braking torque) do not apply. The closed loop in the longitudinal deceleration controller outside the brake system then increases the brake demand or the target vehicle longitudinal deceleration. If the brake demand corrected by the longitudinal deceleration controller thereby exceeds the second brake demand limit value, then it is in the second brake demand range and the brake pressure is generated according to the second characteristic curve section of the characteristic curve. For example, the second characteristic curve section has a greater slope than the first characteristic curve section. Consequently, in the case of an under-braked vehicle, any further increase in the brake demand, in this case caused for example by the longitudinal deceleration controller, leads to what may be a linear increase in the output brake pressure because of the steeper course or gradient of the second characteristic curve section. In this case, the vehicle deceleration can still be controlled by the longitudinal deceleration controller by varying the brake demand, while at the same time ensuring that, for example, the maximum applicable brake pressure can be achieved.

In another example, it is assumed that there is a fault in a component of the braking system, for example a software error or a hardware defect in a primary electronic brake control unit. When the longitudinal deceleration controller then requests braking from the braking system, however, no braking pressure is generated by the braking system from the primary brake control unit affected by the defect. The longitudinal deceleration controller then very quickly increases the brake demand up to the third brake demand range because no actual deceleration of the vehicle could be detected and therefore vehicle braking has failed to occur. The brake system then controls the maximum brake pressure into all brake cylinders in the third brake demand range by a redundant secondary electronic brake controller of the brake system. This may be done with all available solenoid valve devices/actuators that can supply brake pressure to the brake cylinders. Therefore, all redundant electronic brake controllers, solenoid valve devices, and brake cylinders may then be used to increase the likelihood of brake application and to compensate for defects in hardware or software. The determination of the brake pressure in this is then just not done here via the first or second characteristic curve sections, i.e. by individual calculations or assignments, but may be done in a third characteristic curve section, in which the maximum (applicable) brake pressure is automatically assigned to each brake request or demand. On the one hand, this allows potential errors in the software and hardware to be compensated. Further, time-consuming individual calculations and assignments between brake demands and brake pressures can be omitted because the maximum brake pressure is automatically assigned to each brake request or demand. In particular, the brake system and its components are not checked for defects because this would take too much time. However, functions of the brake system that ensure vehicle stability, for example by controlling the braking pressure individually for each wheel, e.g. as part of a brake slip control system (ABS), traction control system (ASR) or vehicle dynamics control system (ESP), can remain active depending on the availability of the corresponding hardware. Such availability is given, for example, if corresponding routines are implemented in the redundant, secondary brake control unit.

In summary, therefore, the invention has the following advantages:

-   -   Avoidance of an underbraked vehicle for high target         decelerations,     -   Ensuring controllable brake pressure up to the maximum brake         pressure,     -   Improvement of controller stability and controller speed         compared to a structure with controller cascade,     -   Reducing the risk of an unbraked vehicle.

The third brake demand limit value may be smaller in amount or magnitude than the amount or magnitude of the maximum brake demand.

Furthermore, it may be provided that the first characteristic curve section and/or the second characteristic curve section has (have) a linear course. The second characteristic curve section can also directly follow the first characteristic curve section.

Particularly, the first characteristic curve section and/or the second characteristic curve section may be formed or specified as a function of a vehicle load of the vehicle, the vehicle load being determined or estimated.

Particularly, a third characteristic curve section of the characteristic curve may be defined or specified which extends between the third support point and a fourth support point and automatically assigns the maximum brake pressure to each brake demand in a third brake demand range or area (III), with the fourth support point assigning the maximum brake pressure and the maximum brake demand to one another. This third characteristic curve section therefore does not actually have any characteristic property in the strict sense, because it automatically assigns the maximum (applicable) brake pressure to each brake demand within the third brake demand area (III).

Also, the minimum brake demand and the minimum brake pressure can each correspond to the value zero, so that the first interpolation or support point of the characteristic curve simultaneously represents the “origin” of the characteristic curve.

A second aspect of the invention presents at least one characteristic curve that represents a relationship between a brake pressure and a brake demand in a pressure fluid actuated brake system, the characteristic curve having been defined or determined according to a method written above.

A third aspect of the invention presents a method of operating a pressurized fluid-actuated braking system of a vehicle, wherein at least one brake cylinder is adapted to be pressurized with a pressurized fluid under a braking pressure, and wherein the braking pressure is determined on the basis of at least one characteristic curve described above or at least one characteristic curve defined according to a method described above that reflects a relationship between the braking pressure and a braking demand, comprising at least the following steps:

-   -   a) determining the brake pressure based on the first         characteristic curve section or the second characteristic curve         section depending on the brake demand at least by:         -   a1) check whether the brake demand is in the first brake             demand range or area (I) or in the second brake demand area             or range (II), and         -   a2) if the brake demand is in the first brake demand range             (I), then determining the brake pressure according to the             first characteristic curve section, and         -   a3) if the brake demand is in the second brake demand area             (II), then determining the brake pressure according to the             second characteristic curve section, and then     -   b) applying the determined brake pressure to the at least one         brake cylinder.

As already explained above, the braking demand, on the basis of which the brake pressure is determined using the characteristic curve, can be generated by a vehicle longitudinal deceleration control system, a driver assistance system or by an autonomous vehicle control system. In particular, the vehicle longitudinal deceleration control can be integrated into the driver assistance system or into the autonomous vehicle control system.

The vehicle longitudinal deceleration control system may adjusts an estimated or determined actual vehicle longitudinal deceleration to a setpoint or target vehicle longitudinal deceleration, with the braking demand, on the basis of which the braking pressure is determined using the characteristic curve, being formed as a function of the setpoint or target vehicle longitudinal deceleration. The actual vehicle longitudinal deceleration is measured, for example, by at least one longitudinal deceleration sensor.

The brake pressure may be determined on the basis of the third characteristic curve section if the brake demand lies in the third brake demand area (III), and then the at least one brake cylinder is (automatically) applied with the maximum brake pressure.

This embodiment refers to the example already described above, according to which it is assumed that there is a fault in a component of the braking system, for example a software fault or a hardware defect in a primary electronic brake control unit. However, when the longitudinal deceleration controller then requests braking from the brake system, no brake pressure is generated from the brake system by the primary electronic brake controller affected by the defect. The longitudinal deceleration controller then very quickly increases the brake demand up to the third brake demand range because no actual deceleration of the vehicle could be detected and therefore vehicle braking has failed to occur. When a brake demand is made in this third brake demand range, the maximum (applicable) brake pressure is then automatically applied to at least one brake cylinder. This saves time because there is no longer any individual assignment between the respective brake demand and the brake pressure, but instead the maximum brake pressure is (automatically) requested and applied to the at least one brake cylinder.

The brake system may comprise at least two independent electronic brake controllers, a first electronic brake controller and a second electronic brake controller, and at least one solenoid valve arrangement or device independently controlled by the first electronic brake controller and the second electronic brake controller, wherein the characteristic curve is implemented in the first electronic brake control unit and in the second electronic brake control unit, and the brake request or demand is input into the first electronic brake control unit and the second electronic brake control unit, and the first electronic brake control unit and the second electronic brake control unit, depending on the brake demand, independently of one another electrically control the at least one solenoid valve arrangement in order to generate the brake pressure.

The at least one solenoid valve arrangement can be formed in particular in a pressure control module which is electrically controlled by the first and/or second electronic brake control unit in order to control a regulated service brake pressure on the basis of a reservoir pressure originating from a pressure reservoir. The electrical control is used to specify a target service brake pressure. For this purpose, the pressure control module has a local electronic control unit which receives the signal for the setpoint braking pressure, the solenoid valve device, in particular as an inlet/outlet valve combination, and a relay valve which is pneumatically controlled by the solenoid valve device and whose operating output is then used to control the actual service braking pressure, which is measured by an integrated pressure sensor. The measured actual pressure value is then reported to the integrated local electronic control unit of the pressure control module, which then controls the integrated inlet/outlet valve combination to adjust the actual service brake pressure to the target service brake pressure.

Alternatively, the at least one solenoid valve arrangement can also be formed in a parking brake module which is electrically controlled by the first and/or second brake control unit in order to control, for example, a regulated parking brake pressure for passive brake cylinders (spring brake cylinders) on the basis of a reservoir pressure originating from a pressure reservoir.

The procedure may be advanced that

-   -   a) if the brake demand is in the first brake demand range or         area (I) or in the second brake demand range or area (II),         checking whether an electronic brake control device from the         first electronic brake control device or the second electronic         brake control device has a defect, and if this is the case, then         the at least one solenoid valve arrangement or device is         controlled by the remaining functional electronic brake control         device which does not have a defect in order to generate the         brake pressure, but     -   b) if the brake demand is in the third brake demand area or         range (III), no check is made as to whether an electronic brake         control device of the first electronic brake control device         and/or the second electronic brake control device has a defect,         and the at least one solenoid valve arrangement or device is         controlled by the first electronic brake control device and by         the second electronic brake control device to generate the brake         pressure.

Feature b) has the particular advantage mentioned above that no time is lost due to the lack of a defect check and the maximum (applicable) brake pressure can then be applied relatively quickly to the at least one brake cylinder.

In the case of feature a), the check as to whether a brake control unit of the first electronic brake control unit and/or the second electronic brake control unit has a defect can be performed by self-monitoring of the first electronic brake control unit and the second electronic brake control unit, or also by external monitoring, in which case the first and second brake control units monitor each other, for example.

As already indicated above, the brake system can be or comprise

-   -   a) an electro-pneumatic service brake system, wherein the at         least one brake cylinder is an active brake cylinder which is         applied by increasing the brake pressure in the application         direction and by decreasing the brake pressure in the release         direction, and/or     -   b) an electro-pneumatic parking brake system, wherein the at         least one brake cylinder is a passive spring brake cylinder         which is applied by increasing the brake pressure in the release         direction and by decreasing the brake pressure in the         application direction.

A fourth aspect of the invention presents a pressurized fluid actuated brake system of a vehicle, wherein at least one brake cylinder is operable to be pressurized with a pressurized fluid under a braking pressure, wherein it is operated according to the method described above.

An embodiment of the invention is shown below in the drawings and explained in more detail in the following description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows an example of a characteristic curve showing a relationship between a brake demand and a brake pressure.

FIG. 2 shows a schematic representation of an autonomous driving system showing a longitudinal deceleration control system and a braking system controlled by the longitudinal deceleration control system, as well as a vehicle that can be braked by the braking system.

FIG. 3 shows a flow chart of an exemplary embodiment of a method for controlling the braking system.

FIG. 4 shows a braking system according to an exemplary embodiment.

DETAILED DESCRIPTION

In FIG. 4, a pressure-fluid-actuated electronically controlled service brake system 100 of, for example, a heavy commercial vehicle is shown in highly schematic form, which is configured, for example, as an electro-pneumatic brake system and, in particular, as an electro-pneumatic brake pressure-controlled brake system (EBS).

The service brake system 100 here has, for example, at least two independent electronic brake control units, a first electronic brake control unit Brake-ECU 1 and a second electronic brake control unit Brake-ECU 2, which control the brake control/regulation functions and other higher-level functions such as a brake slip control (ABS), a traction slip control (ASR) and/or a vehicle dynamics control and/or also an axle-by-axle or side-by-side brake pressure distribution (BDV). Since the two electronic brake control units Brake-ECU 1 and Brake-ECU 2 are mutually redundant brake control units in the sense that if one of the electronic brake control units Brake-ECU 1 or Brake-ECU 2 fails, the other one, If one of the electronic brake control units Brake-ECU 1 or Brake-ECU 2 fails, the other, still intact electronic brake control unit Brake-ECU 1 or Brake-ECU 2 executes the brake control/brake regulation functions and the other higher functions, all the relevant software functions in particular are implemented in full in both electronic brake control units Brake-ECU 1 or Brake-ECU 2.

The two electronic brake control units Brake-ECU 1 or Brake-ECU 2 receive here, for example, from a Highly Automated Driving System (HADS) 200 a service brake request or demand signal a_(soll) representing a target vehicle longitudinal deceleration a_(soll) requested as a service brake demand and process this in order to control at least one solenoid valve arrangement or device 1 independently of one another depending on the service brake demand signal a_(soll). For this purpose, a characteristic curve 2 described in more detail later is implemented in the first electronic brake control unit Brake-ECU 1 and in the second electronic brake control unit Brake-ECU 2.

As shown in FIG. 2, the Highly Automated Driving System (HADS) 200 includes a longitudinal deceleration controller 300 that adjusts an actual vehicle longitudinal deceleration a_(ist) measured on the vehicle, for example, using a longitudinal deceleration sensor, to the target vehicle longitudinal deceleration a_(soll) representing the respective service brake demand.

The at least one solenoid valve arrangement 1 of FIG. 4 can be formed in particular in a pressure control module 3 known per se, which is electrically controlled here, for example, by the first and second electronic brake control units Brake-ECU 1 and Brake-ECU 2 in order to control a regulated service brake pressure on the basis of a supply pressure originating from a pressure reservoir 4. The electrical control by the two electronic brake control units Brake-ECU 1 and Brake-ECU 2 specifies a target service brake pressure. For example, one such pressure control module 3 can be provided for the front axle and one for the rear axle of the vehicle, in particular a single-channel pressure control module on the front axle and a dual-channel pressure control module on the rear axle.

In a known manner, such a pressure control module 3 has an integrated local electronic control unit which receives a signal representing the set service brake pressure from the two electronic brake control units Brake-ECU 1 and Brake-ECU 2, furthermore the solenoid valve device 1, in particular as an inlet/outlet valve combination, as well as a relay valve pneumatically controlled by the solenoid valve device 1, via the operating output of which the actual service brake pressure is then output to at least one brake actuator 5, in this case at least one active service brake cylinder, which is measured by an integrated pressure sensor. The measured actual service brake pressure is then reported to the integrated local electronic control unit of the pressure control module 3, which then controls the integrated inlet/outlet valve combination to adjust the actual service brake pressure to the target service brake pressure. This realizes a service brake pressure control.

The characteristic curve 2 already mentioned above shows a relationship between the service brake pressure p and the service brake demand a_(soll). The characteristic curve 2 therefore assigns a specific service brake pressure p to a specific service brake demand a_(soll), as can be easily imagined from FIG. 1.

In order to form or define the characteristic curve 2 before its actual application or implementation, a service brake demand value range is defined or established for the service brake demand, which comprises a minimum service brake demand, a maximum service brake demand and intermediate values between the minimum service brake demand and the maximum service brake demand. The values of this service brake demand value range can be formed, for example, by a requested deceleration a in m/s² or also by a certain percentage, which then lies, for example, between 0% for the minimum service brake demand and 100% for the maximum service brake demand, with the limits included. In FIG. 1, this service brake demand value range is plotted on the Y axis.

Furthermore, a service brake pressure value range is also specified or defined for the service brake pressure p, which comprises a minimum service brake pressure (e.g. p_(min)=0), a maximum service brake pressure (maximum applicable brake pressure) and intermediate values between the minimum service brake pressure and the maximum service brake pressure (maximum applicable brake pressure). In FIG. 1, this range of service brake pressure values is plotted on the X axis.

A first interpolation or support point 6, 6′, 6″ is then defined by the characteristic curve 2, at which a first service brake demand limit value 8 and a first brake pressure p₁ are assigned to one another, the first service brake demand limit value 8 lying within the service brake demand value range and the first brake pressure p₁ lying within the brake pressure value range, and the first service brake demand limit value 8 representing a minimum service brake demand and the first service brake pressure representing a minimum service brake pressure. In the example of FIG. 1, the first service brake demand limit value 8 is equal to 0 m/s², for example, and the first service brake pressure is equal to 0 bar, for example. The first support point 6 of the characteristic curve 2 therefore may form the origin of the diagram of FIG. 1 here.

Furthermore, a second support point 7, 7′, 7″ of the characteristic curve 2 is defined or determined, at which a second service brake demand limit value 9 and a second brake pressure p² are assigned to one another, the second service brake demand limit value 9 lying within the service brake demand value range and being greater in amount than the amount of the minimum service brake demand but smaller than the amount of the maximum service brake demand. Furthermore, the second service brake pressure p₂ is within the service brake pressure value range and is greater than the minimum service brake pressure but less than the maximum service brake pressure (maximum applicable brake pressure). In this case, the second service brake demand limit value 9 represents, for example, the largest deceleration in terms of magnitude during partial braking.

Furthermore, a first characteristic curve section 2 a, 2 a′, 2 a″ of the characteristic curve 2 is defined or determined, which extends between the first support point 6 and the second support point 8, and which, in a first brake demand range I, represents the relationship between the brake pressure p and the service brake demand a_(soll). The first characteristic curve section 2 a, 2 a′, 2 a″ therefore assigns a specific service brake pressure p here, for example, to a service brake demand a_(soll) of a partial braking.

Furthermore, a third support point 10 of the characteristic curve is also defined, at which a third service brake demand limit value 11 and a third brake pressure p₃ are assigned to each other, wherein the third brake demand limit value 11 lies within the brake demand value range and is greater in amount than the amount of the second brake demand limit value 9 but less than or equal to the magnitude or amount of the maximum demand, and wherein the third brake pressure p₃ lies within the brake pressure value range and is equal to the maximum applicable brake pressure.

Furthermore, a second characteristic curve section 2 b, 2 b′, 2 b″ of the characteristic curve 2 is also defined, which extends between the second support point 7 and the third support point 10, and which, in a second brake demand range II, represents the relationship between the brake pressure p and a brake demand a_(soll).

Particularly, a third characteristic curve section 2 c of the characteristic curve 2 may also be defined, which extends between the third support point 10 and a fourth support point 12 and automatically assigns the maximum brake pressure (maximum applicable brake pressure) to each brake demand a_(soll) within a third brake demand range III, the fourth support point 12 assigning the maximum brake pressure (maximum applicable brake pressure) and the maximum brake demand to each other. In this third characteristic curve section 2 c, the maximum applicable brake pressure is automatically assigned to each brake demand a_(soll) within the third brake demand area III, so that the third characteristic curve section represents a vertical line, as shown in FIG. 1.

As further shown in FIG. 1, the courses of the first, second and third characteristic curve sections 2 a, 2 a′, 2 a″, 2 b, 2 b′, 2 b″ and 2 c may be linear, whereby the slopes of the first and second characteristic curve sections 2 a, 2 a′, 2 a″, 2 b, 2 b′, 2 b″ may differ. This also applies, for example, with inclusion of the third characteristic curve section 2 c.

Also, for example, different characteristic curves are defined for different load conditions of the commercial vehicle, whereby in FIG. 1, the large dashed line symbolizes the first, second and third characteristic curve sections 2 a′, 2 b′, 2 c of a lightly loaded commercial vehicle, the small dashed line symbolizes the first, second and third characteristic curve sections 2 a, 2 b, 2 c of a medium loaded commercial vehicle and the dash-dotted lines symbolize the first, second and third characteristic curve sections 2 a″, 2 b″, 2 c of a fully loaded commercial vehicle. Depending on the load, the slope of the linear first and second characteristic curve sections 2 a, 2 b therefore varies, while the third characteristic curve section 2 c is the same for all load conditions, because the maximum brake pressure (maximum applicable brake pressure) may be always requested there.

As already indicated above, the characteristic curve 2 or the load-dependent characteristic curves 2 a, 2 b, 2 c are respectively stored in a memory area of the first and second electronic brake control unit Brake-ECU 1, Brake-ECU 2.

FIG. 3 shows a flow chart of an exemplary embodiment of a method for operating the pressure fluid-actuated service brake system 100. In a step 101, a brake demand signal according to a brake demand a_(soll) of the Highly Automated Driving System (HADS) 200 is input to the first and second electronic brake control units Brake-ECU 1 and Brake-ECU 2. This brake demand signal is verified in an optional step 102. In a subsequent step 103, it is verified whether the brake demand a_(soll) represented by the brake demand signal is in the first brake demand range I or in the second brake demand range II (see FIG. 1). If this is the case, i.e. the brake demand a_(soll) is either in the first brake demand range I or in the second brake demand range II, it is checked whether the first electronic brake control unit Brake-ECU 1 has a defect. If this is not the case, it is checked in a subsequent step 105 whether the brake demand a_(soll), which is represented by the brake demand signal, lies in the first brake demand range I or alternatively in the second brake demand range II.

If the brake demand lies in the first brake demand range I, then the service brake pressure p is determined in a step 106 according to the first characteristic curve section 2 a, 2 a′, 2 a″. If, however, the service brake demand a_(soll) lies in the second brake demand range II, then in a step 107 the service brake pressure p is determined according to the second characteristic curve section 2 b, 2 b′, 2 b″. The optionally additionally executed common step 108 then comprises a wheel-individual control or regulation of the service brake pressure p. The service brake pressure p determined on the basis of characteristic curve 2 is then applied to the at least one brake actuator 5.

This service brake pressure p then provides an actual longitudinal deceleration a_(ist) of the commercial vehicle in the at least one service brake actuator 5, which is then adapted by the longitudinal deceleration controller 300 of FIG. 2 to the target longitudinal deceleration a_(soll) corresponding to the braking requirement.

If it is determined in step 104 that the first electronic brake control unit Brake-ECU 1 has a defect, the at least one solenoid valve device 1 or the at least one pressure control module 3 cannot be actuated by the first electronic brake control unit Brake-ECU 1 in accordance with step 109 in order to generate the service brake pressure p by controlling the at least one pressure control module 3 or the at least one solenoid valve device 1. In this case, the intact second electronic brake control unit Brake-ECU 2, which is redundant with respect to the first electronic brake control unit Brake-ECU 1, then ensures implementation of the service brake demand in accordance with steps 105, 106 or 107 and 108, as described above.

If it is determined in step 103 that the brake demand or the target vehicle longitudinal deceleration a_(soll) is neither in the first brake demand range I nor in the second brake demand range II but in the third brake demand range III, no check of the first electronic brake control unit Brake-ECU 1 and/or the second electronic brake control unit Brake-ECU 2 or further components of the service brake system 100 takes place. Rather, as shown in FIG. 1, the maximum brake pressure (maximum applicable pressure) is then assigned to each brake demand a_(soll) in the third brake demand area III, which is then generated by the at least one pressure control module 3 or the at least one solenoid valve device 1 based on the reservoir pressure of the pressure reservoir 4 and is fed into the at least one brake actuator 5.

The invention is not limited to an application to a service brake system 100, it can readily be applied to a park brake system to control/regulate parking brake pressure. Because of the passive brake spring cylinders as normally used in such a parking brake system, the maximum pressure becomes the minimum pressure and vice versa.

The List of References is as follows:

-   1 solenoid valve device -   2 characteristic curve (map) -   2 a, 2 a′, 2 a″ first characteristic curve section -   2 b, 2 b′, 2 b″ second characteristic curve section -   2 c third characteristic curve section -   3 pressure regulator -   4 pressure reservoir -   5 brake actuator -   6 first support point -   7 second support point -   8 first brake demand limit value -   9 second brake demand limit value -   10 third support point -   11 third brake demand limit value -   12 fourth support point -   100 service brake system -   200 highly automated driving system -   300 longitudinal deceleration controller -   Brake-ECU1 first brake control unit -   Brake-ECU2 second brake control unit -   a_(ist) actual vehicle longitudinal deceleration -   a_(soll) target vehicle longitudinal deceleration (brake demand) -   I first brake demand range -   II second brake demand range -   III third brake demand range 

What is claimed is:
 1. A method for defining at least one characteristic curve which, in a pressure-actuated brake system of a vehicle, represents a relationship between a brake pressure and a brake demand, the method comprising: a) specifying a brake demand value range for the brake demand, which includes a minimum brake demand, a maximum brake demand, and intermediate values between the minimum brake demand and the maximum brake demand, b) specifying a brake pressure value range for the brake pressure, which includes a minimum brake pressure, a maximum brake pressure and intermediate values between the minimum brake pressure and the maximum brake pressure, c) defining at least two characteristic curve sections of the characteristic curve, by: c1) defining a first support point of the characteristic curve, at which a first brake demand limit value and a first brake pressure are assigned to one another, the first brake demand limit value lying within the brake demand value range and the first brake pressure lying within the brake pressure value range, and the first brake demand limit value representing a minimum brake demand and the first brake pressure representing a minimum brake pressure, c2) defining a second support point of the characteristic curve, at which a second brake demand limit value and a second brake pressure are associated with each other, wherein the second brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the minimum brake demand but smaller than the amount of the maximum brake demand, and wherein the second brake pressure is within the brake pressure value range and is greater than the minimum brake pressure but less than the maximum brake pressure, c2) defining a first characteristic curve section of the characteristic curve which extends between the first support point and the second support point and which, in a first brake demand range, represents the relationship between the brake pressure and the brake demand, c3) defining a third support point of the characteristic curve, at which a third brake demand limit value and a third brake pressure are associated with each other, wherein the third brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the second brake demand limit value but less than or equal to the amount of the maximum brake demand, and wherein the third brake pressure lies within the brake pressure value range and is equal to the maximum brake pressure, c4) defining a second characteristic curve section of the characteristic curve which extends between the second support point and the third support point and which, in a second brake demand range, represents the relationship between the brake pressure and a brake demand.
 2. The method of claim 1, wherein the third brake demand limit is smaller in amount than the amount of the maximum brake demand.
 3. The method of claim 1, wherein the first characteristic curve section and/or the second characteristic curve section has a linear course.
 4. The method of claim 1, wherein the second characteristic curve section directly adjoins the first characteristic curve section.
 5. The method of claim 1, wherein the minimum brake demand and the minimum brake pressure are each equal to zero.
 6. The method of claim 1, wherein a third characteristic curve section of the characteristic curve is defined, which extends between the third support point and a fourth support point and automatically assigns the maximum brake pressure to each brake demand in a third brake demand area, the fourth support point assigning the maximum brake pressure and the maximum brake demand to each other.
 7. The method of claim 6, wherein the first characteristic curve section and/or the second characteristic curve section and/or the third characteristic curve section are formed or specified as a function of a vehicle load of the vehicle, the vehicle load being determined or estimated.
 8. A characteristic curve, comprising: a curve, which, in a pressure-fluid-actuated brake system, represents a relationship between a brake pressure and a brake demand; wherein the curve has been defined or determined by performing the following: a) specifying a brake demand value range for the brake demand, which includes a minimum brake demand, a maximum brake demand, and intermediate values between the minimum brake demand and the maximum brake demand, b) specifying a brake pressure value range for the brake pressure, which includes a minimum brake pressure, a maximum brake pressure and intermediate values between the minimum brake pressure and the maximum brake pressure, c) defining at least two characteristic curve sections of the characteristic curve, by: c1) defining a first support point of the characteristic curve, at which a first brake demand limit value and a first brake pressure are assigned to one another, the first brake demand limit value lying within the brake demand value range and the first brake pressure lying within the brake pressure value range, and the first brake demand limit value representing a minimum brake demand and the first brake pressure representing a minimum brake pressure, c2) defining a second support point of the characteristic curve, at which a second brake demand limit value and a second brake pressure are associated with each other, wherein the second brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the minimum brake demand but smaller than the amount of the maximum brake demand, and wherein the second brake pressure is within the brake pressure value range and is greater than the minimum brake pressure but less than the maximum brake pressure, c2) defining a first characteristic curve section of the characteristic curve which extends between the first support point and the second support point and which, in a first brake demand range, represents the relationship between the brake pressure and the brake demand, c3) defining a third support point of the characteristic curve, at which a third brake demand limit value and a third brake pressure are associated with each other, wherein the third brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the second brake demand limit value but less than or equal to the amount of the maximum brake demand, and wherein the third brake pressure lies within the brake pressure value range and is equal to the maximum brake pressure, c4) defining a second characteristic curve section of the characteristic curve which extends between the second support point and the third support point and which, in a second brake demand range, represents the relationship between the brake pressure and a brake demand.
 9. A method for operating a pressure-medium-actuated brake system of a vehicle, in which at least one brake cylinder can be acted upon by a pressure medium which is under a braking pressure, and in which the braking pressure represents a relationship between the braking pressure and a braking demand, the method comprising: c) determining the brake pressure based on the first characteristic curve section or the second characteristic curve section depending on the brake demand at least by: a1) checking whether the brake demand is in the first brake demand range or in the second brake demand range, and a2) if the brake demand is in the first brake demand range, then determining the brake pressure according to the first characteristic curve section, and a3) if the brake demand lies in the second brake demand range, then determining the brake pressure according to the second characteristic curve section, and then d) applying the determined brake pressure to the at least one brake cylinder; wherein the characteristic curve, which in a pressure-actuated brake system of a vehicle, represents a relationship between a brake pressure and a brake demand, is determined by the following: e) specifying a brake demand value range for the brake demand, which includes a minimum brake demand, a maximum brake demand, and intermediate values between the minimum brake demand and the maximum brake demand, f) specifying a brake pressure value range for the brake pressure, which includes a minimum brake pressure, a maximum brake pressure and intermediate values between the minimum brake pressure and the maximum brake pressure, g) defining at least two characteristic curve sections of the characteristic curve, by: c1) defining a first support point of the characteristic curve, at which a first brake demand limit value and a first brake pressure are assigned to one another, the first brake demand limit value lying within the brake demand value range and the first brake pressure lying within the brake pressure value range, and the first brake demand limit value representing a minimum brake demand and the first brake pressure representing a minimum brake pressure, c2) defining a second support point of the characteristic curve, at which a second brake demand limit value and a second brake pressure are associated with each other, wherein the second brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the minimum brake demand but smaller than the amount of the maximum brake demand, and wherein the second brake pressure is within the brake pressure value range and is greater than the minimum brake pressure but less than the maximum brake pressure, c2) defining a first characteristic curve section of the characteristic curve which extends between the first support point and the second support point and which, in a first brake demand range, represents the relationship between the brake pressure and the brake demand, c3) defining a third support point of the characteristic curve, at which a third brake demand limit value and a third brake pressure are associated with each other, wherein the third brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the second brake demand limit value but less than or equal to the amount of the maximum brake demand, and wherein the third brake pressure lies within the brake pressure value range and is equal to the maximum brake pressure, c4) defining a second characteristic curve section of the characteristic curve which extends between the second support point and the third support point and which, in a second brake demand range, represents the relationship between the brake pressure and a brake demand.
 10. The method of claim 9, wherein the brake demand, based on which the brake pressure is determined using the characteristic curve, is generated by a vehicle longitudinal deceleration control system, a driver assistance system and/or by an autonomous vehicle control system.
 11. The method of claim 10, wherein the vehicle longitudinal deceleration control controls an estimated or determined actual vehicle longitudinal deceleration to a target vehicle longitudinal deceleration, wherein the brake demand, based on which the brake pressure is determined using the characteristic curve, being formed as a function of the target vehicle longitudinal deceleration.
 12. The method of claim 9, wherein the brake pressure is determined based on the third characteristic curve section if the brake demand lies in the third brake demand range, and then the at least one brake cylinder is acted upon with the maximum brake pressure.
 12. The method of claim 9, wherein the brake system comprises at least two independent electronic brake control units, a first electronic brake control unit and a second electronic brake control unit, and at least one solenoid valve device controlled independently by the first electronic brake control unit and the second electronic brake control unit, wherein the characteristic curve is implemented in the first electronic brake control unit and in the second electronic brake control unit, and wherein the braking demand is input into the first electronic brake control unit and into the second electronic brake control unit, and wherein the first electronic brake control unit and the second electronic brake control unit electrically actuate the at least one solenoid valve device independently of one another as a function of the brake demand, to generate the brake pressure.
 14. The method of claim 12, wherein: a) if the brake demand is in the first brake demand area or in the second brake demand area, it is checked whether an electronic brake control unit of the first electronic brake control unit or the second electronic brake control unit has a defect, and if this is the case, then the at least one solenoid valve device is controlled by the remaining functional electronic brake control unit which has no defect to generate the brake pressure, but b) if the brake demand is in the third brake demand area, no check is made whether an electronic brake control device of the first electronic brake control device and/or the second electronic brake control device is defective, and the at least one solenoid valve device is actuated by the first electronic brake control device and/or by the second electronic brake control device to generate the brake pressure.
 15. The method of claim 14, wherein the check as to whether an electronic brake control unit of the first electronic brake control unit and/or the second electronic brake control unit has a defect is carried out by self-monitoring of the first electronic brake control unit and the second electronic brake control unit, or by external monitoring, the first and second electronic brake control units monitoring each other.
 16. The method of claim 8, wherein the braking system includes: a) an electro-pneumatic service brake system, wherein the at least one brake cylinder is an active brake cylinder which is applied by increasing the brake pressure in the application direction and by decreasing the brake pressure in the release direction, and/or b) an electro-pneumatic parking brake system, wherein the at least one brake cylinder is a passive spring brake cylinder which is applied by increasing the brake pressure in the release direction and by decreasing the brake pressure in the application direction.
 17. A pressure medium-actuated brake system of a vehicle, comprising: at least one brake cylinder, which can be acted upon by a pressure medium which is under a brake pressure; wherein the at least one brake cylinder is controlled by performing the following: c) determining the brake pressure based on the first characteristic curve section or the second characteristic curve section depending on the brake demand at least by: a1) checking whether the brake demand is in the first brake demand range or in the second brake demand range, and a2) if the brake demand is in the first brake demand range, then determining the brake pressure according to the first characteristic curve section, and a3) if the brake demand lies in the second brake demand range, then determining the brake pressure according to the second characteristic curve section, and then d) applying the determined brake pressure to the at least one brake cylinder; wherein the characteristic curve, which in a pressure-actuated brake system of a vehicle, represents a relationship between a brake pressure and a brake demand, is determined by the following: e) specifying a brake demand value range for the brake demand, which includes a minimum brake demand, a maximum brake demand, and intermediate values between the minimum brake demand and the maximum brake demand, f) specifying a brake pressure value range for the brake pressure, which includes a minimum brake pressure, a maximum brake pressure and intermediate values between the minimum brake pressure and the maximum brake pressure, g) defining at least two characteristic curve sections of the characteristic curve, by: c1) defining a first support point of the characteristic curve, at which a first brake demand limit value and a first brake pressure are assigned to one another, the first brake demand limit value lying within the brake demand value range and the first brake pressure lying within the brake pressure value range, and the first brake demand limit value representing a minimum brake demand and the first brake pressure representing a minimum brake pressure, c2) defining a second support point of the characteristic curve, at which a second brake demand limit value and a second brake pressure are associated with each other, wherein the second brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the minimum brake demand but smaller than the amount of the maximum brake demand, and wherein the second brake pressure is within the brake pressure value range and is greater than the minimum brake pressure but less than the maximum brake pressure, c2) defining a first characteristic curve section of the characteristic curve which extends between the first support point and the second support point and which, in a first brake demand range, represents the relationship between the brake pressure and the brake demand, c3) defining a third support point of the characteristic curve, at which a third brake demand limit value and a third brake pressure are associated with each other, wherein the third brake demand limit value lies within the brake demand value range and is greater in amount than the amount of the second brake demand limit value but less than or equal to the amount of the maximum brake demand, and wherein the third brake pressure lies within the brake pressure value range and is equal to the maximum brake pressure, c4) defining a second characteristic curve section of the characteristic curve which extends between the second support point and the third support point and which, in a second brake demand range, represents the relationship between the brake pressure and a brake demand.
 18. The pressure-medium operated brake system of claim 17, wherein the pressure medium-actuated brake system includes at least two independent electronic brake control units, a first electronic brake control unit and a second electronic brake control unit, and at least one solenoid valve device independently controlled by the first electronic brake control unit and the second electronic brake control unit, wherein the characteristic curve is implemented in the first electronic brake control unit and in the second electronic brake control unit, and wherein the brake demand is input into the first electronic brake control unit and into the second electronic brake control unit, and wherein the first electronic brake control unit and the second electronic brake control unit electrically actuate the at least one solenoid valve device independently of one another as a function of the brake demand, to generate the brake pressure. 